Liquid crystal display driver

#The present invention relates to Liquid Crystal Displays (LCD) and, more particularly, to LCD drivers.

#Liquid Crystal Displays (LCDs) are used in many applications where it is desired to display information on a display panel. FIG. 2 illustrates a conventional liquid crystal display 10. Basically, a sandwich of liquid crystals 16 lies between a front electrode panel 26 and a backplane electrode panel 18. Front electrode panel 26 may include several numerical or alphanumerical digits and characters that are formed by individual light-transparent units known as segment electrodes. For example, a numerical digit may be formed of seven segment electrodes 14. Depending on the number desired to be displayed, one or more of the segment electrodes may appear dark. The liquid crystal display further includes a front vertical light filter 12 and a rear horizontal light filter 22. The front vertical filter receives external light, which is randomly polarized, and passes the light rays that are substantially vertically polarized. Likewise, the rear horizontal filter is configured to pass light rays that are substantially horizontally polarized.

#Behind horizontal filter 22 lies a mirror 24 that reflects the light passing through the horizontal filter. The operation of liquid crystal displays is well-known and described in, Electronics, Multiplexing Liquid Crystal Displays, by Paul Smith (May 25, 1978), incorporated herein by reference.

#The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with features, objects, and advantages thereof may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

#FIG. 1 is a schematic diagram illustrating one embodiment of a liquid crystal display (LCD) driver in accordance with the present invention.

#FIG. 2 is an exploded illustration of some elements that form a liquid crystal display (LCD).

#FIG. 3 illustrates an example of a wiring arrangement for applying voltage or current signals to segment and backplane electrodes of a liquid crystal display, such as LCD 10 illustrated in FIG. 2, although the invention is not limited in scope to this particular wiring arrangement. This arrangement has been described in the previously cited reference, Electronics, Multiplexing Liquid Crystal Displays, by Paul Smith (May 25, 1978), and incorporated herein by reference. A predetermined number of numerical digits, such as 60, 62, and 64 with corresponding backplane electrodes, such as 20, 50 and 52, respectively, are coupled together so as to receive multiplexed signals, as will be explained in more detail hereinafter. Each numerical digit is formed of seven segment electrodes. For one particular arrangement, groups of four numerical digits are coupled together (not shown). However, the invention is not limited in scope to groups of four numerical digits and up to n numerical digits may be coupled together, where n is a positive integer.

#Each segment electrode of a numerical digit is coupled to corresponding segment electrodes of the remaining digits. For example, segment electrode 54 of numerical digit 60 is coupled to segment electrode 56 of numerical digit 62, to segment electrode 56 of numerical digit 64 and so forth. Thus, the segment electrodes of each group of four numerical digits share seven terminals 34a to 34g to receive electrical signals intended to control the orientation of liquid crystal molecules disposed between the segment electrodes and the backplane electrodes. Each backplane electrode, such as 20, 50 and 52, receives an electrical signal via signal lines 66, 68 and 70, respectively. The electrical signals are applied to the backplane electrodes to control the orientation of liquid crystal molecules disposed between the segment electrodes and the backplane electrodes.

#As mentioned previously, in order to increase the life of the liquid crystal display, it is desirable to apply a time varying (AC) voltage or current signal to both segment electrodes and backplane electrodes. Thus, a nominal AC voltage signal 70 is continually applied to terminals 34 corresponding to front segment electrodes of liquid crystal display. Likewise, a nominal AC signal, as illustrated in FIG. 4, is applied substantially simultaneously to signal lines, such as 66, 68 and 70. It will be appreciated that the amplitude of these nominal AC signals is small enough to not affect the orientation of liquid crystal molecules, and is large enough to prevent the crystals from deteriorating in a substantially short period of time.